The present invention relates generally to turbine engines and more particularly, to a wear-indicating system for use with turbine engines.
At least some known turbines have a defined flow path that includes, in serial-flow relationship, an inlet, a turbine, and an outlet. At least some known steam turbines also include a plurality of stationary diaphragms that direct a flow of steam towards a rotor assembly that includes at least one row of turbine buckets (blades) that are circumferentially-spaced about a rotor disk. Steam channeled to the rotor assembly from the diaphragm assembly impacts airfoils of the turbine buckets to induce rotation of the rotor assembly.
The environment inside the steam engine may facilitate wear and erosion of the rotor assembly, particularly the bucket airfoils. Over time, erosion of airfoils result in rough, uneven airfoil surfaces that alter steam flow paths that may reduce turbine efficiency and/or limit turbine capacity. Erosion of intermediate and low-pressure airfoils is usually caused by water in the steam. For example, operation below design inlet steam temperature or at low load can create condensation in these stages that may cause erosion. Moreover, the entrainment of erosive materials in the steam, such as iron oxide, may also erode the turbine airfoils, particularly at the high-pressure end of the turbine.
Typically, to inspect a turbine, a boroscope is inserted into the interior of the turbine to determine an amount of erosion of the buckets. However, visual inspections enable only qualitative determinations of the amount of erosion. More reliable and accurate quantitative determination of the amount of erosion are generally not possible without disassembly of the turbine. The inability to make a reliable and accurate quantitative determination of the amount of erosion using a boroscope is due, at least in part, to non-standardized magnification of boroscopes and to the lack of measurement references inside the turbine. However, increasing the reliability and accurateness of erosion inspections of internal components of a turbine may facilitate extending the time between outages and improving the efficiency of the turbine.